Recent developments in the field of vaccine production have created the need for large scale manufacturing. Robust and high yield processes are needed to support the world with sufficient amounts of (recombinant) vaccines to combat infectious diseases.
Vaccines against infectious diseases can be based on recombinant adenovirus particles. For that reason, great efforts are being put into the optimization of cell based processes for adenovirus production. Cells are being cultured at increasing densities and subsequently infected in order to obtain higher total virus yields. Such high cell density processes are being disclosed in e.g. WO 2010/060719 of Crucell Holland B V, and in Yuk et al. (2004). A process for the production of large concentrations of recombinant adenovirus was described therein. This optimized process relies on the ability to infect cultures at high cell density (e.g. higher than 5×106 cells/ml) with preservation of a high virus productivity per cell. Herewith, it offers a method to obtain a harvested virus solution with high virus concentration in a single bioreactor. Typical virus particle (VP) yields of said processes are about 1.5-2.5×1012 VP/mL.
Processes wherein cells are cultured at high densities are prone to the accumulation of high amounts of cell debris and host cell DNA. These contaminants have to be discarded further down the purification process, which is a cumbersome operation. A method for discarding host cell DNA from a harvested cell culture was disclosed previously in U.S. Pat. No.7,326,555. The method consists of selectively precipitating host cell DNA away from the cell culture. A selective precipitating agent could specifically bind to host cell DNA and leave adenovirus particles unprecipitated. The method in this reference however has only been described for cell cultures with low cell density, wherein cell debris and host cell DNA are present in low quantities.
It was not known hitherto that said process could be applied in a culture containing high cell densities. To the contrary, from the prior art a strong suggestion could be inferred that a precipitating agent as used in said method would not selectively precipitate host cell DNA away from the culture and would precipitate virus particles when used at high concentrations (Goerke et al. 2004).
The adenovirus-containing cell culture harvests are generally further processed in order to obtain purified adenovirus. A clarification step using e.g. depth filtration and/or tangential flow filtration (TFF) is usually included in said purification process. The use of TFF requires a relatively clean harvest, that is, containing limited quantities of cell debris or other impurities such as e.g. host cell DNA. An excess of said impurities could possibly block the filters. As a consequence, clarification by TFF is commonly used further down the purification process e.g. as a third or fourth process step.
Separation of adenovirus from an adenovirus-containing cell suspension directly after harvest, using tangential flow filtration was previously described in e.g. EP1371723. However, the adenovirus was grown on adherent cells, which remained in the bioreactor after harvesting. Therefore, the virus containing suspension that was further processed contained very low concentrations of cell debris and host cell DNA. WO2006/052302 also describes the use of TFF directly after harvest. However, the cell densities of the virus-containing harvest used therein were much lower then 5×106 cells/ml. As disclosed herein, the use of TFF in the clarification step directly after harvest is not feasible for cell cultures containing high cell densities.
Since cell culture processes are being up-scaled and cells are being cultured at increasing densities, there is a need in the industry for downstream processes that enable the treatment of high cell density suspensions. This applies in particular to the field of adenovirus production.